1. Field of the Invention
This invention relates generally to foundry mold and core blowing machines incorporating a sand/resin mixture. More particularly this invention relates to the mixing chamber or nozzle of such a blowing machine.
2. Description of the Prior Art
In the foundry art, cores or molds are made from mixtures of aggregate materials, ordinarily sand, which have been combined with polymerizable or curable material. After the sand and binder have been mixed, the resulting sand/binder mix is rammed, blown or otherwise introduced into a pattern, thereby causing it to assume the shape defined by the adjacent surfaces of the pattern. Polymerization or curing is induced by one means or another (catalyst, heat, etc.) thereby converting the formed, uncured, plastic, foundry sand mix into a hard, solid, cured state.
In recent years an increasing demand for dimensionally accurate cores has been felt by the foundry industry. Another pressure felt by the industry is the ever present need to reduce the core or mold cure time to a minimum. One way to reduce the machine cycle time and thereby increase production is to reduce the curing time of the curable resin.
In response to this need, the foundry industry has developed machines, processes and resin/catalyst mixtures that allow increasingly rapid cure and correspondingly short machine recycle time. See U.S. Pat. Nos. 3,255,500; 3,494,412 and 3,472,307, which patents are illustrative of the prior art techniques.
One of the methods developed in the prior art is the process of mixing a resin and a catalyst which react rapidly without heat, called the kold box process. The resin and catalyst are independently mixed with two separate charges of sand and then brought together and mixed only at the last minute before blowing the sand/resin/catalyst mixture into the core box. In practice, the sand/resin/catalyst mixture is delivered, after mixing, to a second chamber which is closed off and pressurized to blow the sand into the core box. After a short period at room temperature, the cured core may be removed from the box. Reasonable results in both the areas of dimensional accuracy and minimum recycle time have become possible with improved binders.
A major difficulty that has been encountered in the prior art is that any residual sand/catalyst/resin mixture remaining anywhere in the mixing and blowing chambers of the blow machine cure just as rapidly as the blown core or mold. Once cured, these sand/resin/catalyst residues adhere to the surfaces of the machine and tend to impede the passage of subsequent charges of sand through the machine thereby preventing its proper operation. In addition, if the volume of the charges of the originally prepared sand/resin/catalyst mixture are greater than the volume of the core to be blown, a small amount of overflow remains in the blow nozzle, necessitating swinging the machine aside and cleaning the nozzle before the short time period required for the resin to cure. A final difficulty in the prior art blowing machines arises if, for some reason, the blow operation is interrupted after the sand/resin/catalyst mixture has been mixed and delivered to the blow chamber but before actual blowing into the core box. This mixed charge must be immediately removed and discarded or the mixture will cure within the blow chamber rendering the blow machine inoperable.
One attempted solution to the above-mentioned problems has been to premeasure the sand charges so that there is no excess sand after the blow of the core. This attempted solution has proved unsatisfactory since the measurement process is subject to error and also increases the machine cycle time. If the prepared charge is short, the core fails and the entire charge of sand must be discarded.